Process for preconcentrating



PROCES FOR PRECONCENTRATING LACTAM OILS Gerhard Meier, Leona, Germany,assignor to Veb Lenna- Werke Walter Ulbricht, Leuna, Germany No Drawing.Application June 19, 1956 Serial No. 592,253

16 Claims. (Cl. 260-2393) This invention relates to lactams and moreparticularly to a process for preconcentrating lactam oils obtained bythe Beckmann rearrangement of the oximes of cyclic ketones andsubsequent neutralization.

It is an object of this invention to provide a process .for thepreconcentration of water-containing lactam oils,

wherein a preconcentrated lactam oil is obtained which may be extractedwithout the formation of emulsions.

A further object of the invention is to provide a process for thepreparation of preconcentrated lactam oils from crude lactam oils whichyield lactams in high yield and of very good quality.

Still another object of the invention is the provision of a process forthe preparation of preconcentrated lactam oils which enables theemployment of multi-step extractors for the extraction of thepreconcentrated lactam oils without formation of emulsions.

Finally, it is an object of the invention generally to improve onprocesses for the preconcentration of crude lactam oils as nowcustomarily practised.

Other objects of the invention will become apparent from the followingdescription.

As the result of the Beckmann rearrangement of the oximes of cyclicketones with fuming sulfuric acid or sulfuric acid proper, thecorresponding lactams are first obtained in solution of concentratedsulfuric acid. For the purpose of isolating these lactams, the sulfuricacid is commonly neutralized in technical processes with ammonia water.In this manner an ammonium sulfate liquor is obtained on which thelactams separate as so-called lactam oil. Depending on the nature of thelactam and the particular process and working conditions, this lactamoil has about the following composition:

66-68% of the particular lactam 28-31% of water 1.4-2% of ammoniumsulfate O.2-0.4% of ammonia and 0.1-0.3 of the corresponding ketone Incase it is desired to obtain lactams of high quality and in high yieldfrom these lactam oils, then the latter cannot be distilled in vacuodirectly, but have first to be subjected to an extracting procedure. Itis common practice to employ chlorinated hydrocarbons as extractingagentsin the extracting procedure referred to. However, the use of suchchlorinated hydrocarbons results in the dis advantage that emulsions arefrequently formed in the lactam-poor stages of the extraction, that isafter the major portion of the lactam has already been extracted fromthe oil.

It has been observed that the formation of emulsions can be entirelyavoided by removing from the lactam oil prior to the extraction a partof the water and at the same time the ammonia and ketone containedtherein. With a view to producing the desired effect referred to, it issufficient to remove a quantity of water so that the lactam content inthe oil increases to about 72-78%. It is not advisable to extend thispreconcentration so as to obtain 2,866,785 Patented Dec. 30, 1958 alactam content above since in this case disturbing separation .ofammonium sulfate from the oil may easily occur.

In accordance with this invention the preconcentration of the lactam oilreferred to is effected by passing a gas through the lactam oil in linedistribution and at elevated temperature. In this manner lactams ofexcellent quality are then subsequently obtained. Nitrogen oradvantageously air may be used as the gas referred to. In case air isemployed, impurities contained in the lactam oil are oxidized by the airwhich results in an increased purity of the final product.

According to a further feature of the inventive process the oxidizingeffect and thus the purifying effect may be enhanced still further byadding to the lactam oil small amounts of catalytically active metalsalts, such as for example manganese acetate or cobalt acetate. Thelactams proper are not attacked or otherwise affected by the presence ofsuch metal salts. The inventive process may be performed batchwise orcontinuously.

The inventive process has many advantages besides the fact that thequality of the lactams subsequently obtained is considerably improved.For example, the process requires for its performance very simple andinexpensive apparatus only and is easily carried out. In addition to thefact that the pre-concentration of the lactam oil avoids the formationof emulsions during the subsequent extraction, a considerable purifyingeffect is obtained. v

The process of the invention will now be described by several examples,but it should be understood that these examples are given by way ofillustration rather than by way of limitation, and that many variationsmay be made in for example amounts, temperature and process conditionsin general, without departing in any Way from the spirit and scope ofthe invention.

Example 1 The process to be described was carried out in a relativelywide reaction tube which along its entire length was heated to about C.by a hot water jacket surrounding the tube. 1000 parts by weight of amethyllactam oil were placed into the reaction tube. The methyllactamwas obtained by the Beckmann rearrangement of the oxime ofo-methylcyclohexanone and subsequent neutralization. It contained 68% ofmethyllactam, 28% of water, 1.1% of o-methylcyclohexanone, 1.4% ofammonium-sulfate, and 0.2% of ammonia. Nitrogen was blown through thelactam oil within the tube in fine distribution. The rate of nitrogenblown through the tube was about one hundred times the volume of thelactam oil per hour. After three hours an amount of water had distilledoff which corresponded to a lactam increase in the oil of 9% so that theoil then contained 77% of lactam. The oil was then also entirely devoidof o-methylcyclohexanone and ammonia.

The methyllactam oil thus obtained may be extracted in an extractorcomprising for example 5 steps without any formation of emulsions. Theyield of pure methyllactam amounted to 96%. The methyllactam exhibitedafter distillation in vacuo a permanganate number of 520 seconds. Incontrast thereto methyllactam which has not been subjected to thetreatment described forms milky emulsions in the fourth and fifth stepsof the extractor.

For the purpose of establishing the advantages obtained by the inventiveprocess, water was distilled off at atmospheric pressure from a lactamoil of the same composition as used in this example, until themethyllactam content in the oil had increased to 76%. The thuspretreated oil was readily extracted in a 5-step extractor. Themethyllactam was obtained in a yield of 93% only. After distillation invacuo the methyllactam thus obtained exhibited a permanganate number ofonly 340 seconds.

. Percent Caprolactam 66 Water 3 0.4 Ammonium sulfate 2.1 Ammonia 0.4Cyclohexanone 0.3

Air, preheated to about 100 C., was passed through the reaction tube.The rate of the hot air through the lactam oil was about one hundredtimes the volume of the lactam oil per hour. During its passage throughthe reaction tube the caprolactam content of the lactam oil increased to75-76% and the oil was entirely freed from ammonia and cyclohexanone.The thus concentrated lactam oil left the reaction tube through theoverflow pipe at the bottom end of the reaction tube and was directlyintroduced into the 6-step extractor. During the extraction in theextractor no emulsions were formed. The caprolactam thus obtained in ayield of 98-99% hadafter distillation in vacuo a permanganate number of940 seconds.

For the purpose of establishing the advantages obtained by the inventiveprocess, a lactam oil of the same composition as used in this examplewas distilled at reduced pressure until the caprolactam content in theoil had increased to 76%. This concentrated oil was likewise extractedin a 6-step extractor. however, was only 97% while the permanganatenumber of the caprolactam-after vacuum distillation-was 500 seconds.

Further, a lactam oil of identical composition which has not beensubjected to any preconcentration whatsoever cannot successfully beextracted in a 6-step extractor since formation of emulsions will occuralready in the fourth step. For this reason, only a 3-step extractor canbe employed. The yield in this case amounts to 93-95% only. Thecaprolactam obtained after distillation had a permanganate number of 550seconds.

Example 3 1000 parts by weight of a lactam oil of the same compositionas that employed in Example 2 was treated in the same manner asdescribed in Example 2. However, 0.02% of an aqueous solution ofmanganese acetate of 50% concentration were added to the lactam oilprior to the gas treatment. No emulsion formation occurred duringextraction. The caprolactam was obtained in a yield of 98-99% and had apermanganate number of 1500 seconds and more. Moreover, the caprolactamexhibited an excellent stability to light.

WhatI claim is:

1. A process for the preconcentration of water-containing lactam oilobtained .by the Beckmann rearrangement of oximes of cyclic ketones andsubsequent neutralization, comprising the step of passing a stream ofair through said water-containing oil at elevated temperature until thewater content of said oil has been reduced to a predetermined value.

'2. A process as claimed in claim 1, wherein a catalytically activemetal salt is added to said water-containing lactam oil prior to passingsaid air through said lactam oil, said metal salt being a salt of thegroup of The yield,

salts consisting of manganese acetate and cobalt acctate.

3. A process for the preconcentration of a liquid containing about66-68% of a lactam, 28-31% of water, 1.4-2% of ammonium sulfate, 02-04%of ammonia and 01-03% of a ketone, comprising the step of reducing thecontent of said water and substantially removing said ammonia and saidketone by passing a gas selected from the class consisting of molecularoxygen containing gas and nitrogen through said liquid at elevatedtemperature until the content of said lactam in said liquid has risen toabove 72 but below 4. A process for the preconcentration of a liquidcontaining about 66-68% of a lactam, 28-31% of water, 1.4-2% of ammoniumsulfate, 02-04% of ammonia and 0.3% of a ketone which comprises addingto said liquid a small amount of a catalytically active metal saltselected from the class consisting of manganese acetate and cobaltacetate, reducing the content of said water and substantially removingsaid ammonia and said ltetone by passing air through said liquid atelevated temperature until the content of said lactam in said liquid hasrisen to above 72% but below 80%.

5. A process as claimed in claim 3 wherein said gas is nitrogen.

6. A process for the preconcentration of a liquid containing about66-68% of a lactam, 28-31% of water, 1.4-2% of ammonium sulfate, 02-04%of ammonia and 01-03% of a ketone, comprising the steps of introducingsaid liquid into a reaction tube heated to about C., and passing a gasselected from the class consisting of molecular oxygen containing gasand nitrogen through said reaction tube at a rate of about one hundredtimes the volume of said liquid per hour, until said ammonia and saidketone are removed and the content of said lactam in said liquid isabove 72% but below 80%.

7. A process for the preconcentration of a liquid con taining 66-68% ofa lactam, 28-31% of water, 1.4-2% of ammonium sulfate, 0.2-0.4% ammoniaand 01-03% of a ketone, comprising mixing said liquid with an aqueoussolution of a metal salt selected from the group consisting of manganeseacetate and cobalt acetate, introducing the liquid so formed into areaction tube heated to about 100 C., and passing air through saidreaction tube at a rate of about 100 times the volume of said liquid perhour, until said ammonia and said ketone are removed and the content ofsaid lactam in said liquid is above 72% but below 80%.

8. A process as claimed in claim 6, wherein said gas is preheated priorto being passed through said reaction tube.

9. A process of preconcentrating a methyllactam oil containing about 68%of a methyllactam, 28% of water, 0.2% of ammonia, 1.4% of ammoniumsulfate and 1.1% of o-methylcyc1ohexanone which methyllactam oil isobtained by the Beckmann rearrangement of o-methylcyclohexanone oximeand subsequent neutralization, said process comprising the steps ofintroducing said methyllactam oil into a reaction tube heated to about100 C., and passing nitrogen through said reaction tube at a rate ofabout one hundred times the volume of said methyllactam oil per houruntil said ammonia, said o-methylcyclohexanone and a portion of saidwater have been removed and said methyllactam comprises about 77% ofsaid methyllactam oil.

10. A process of preconcentrating a caprolactam oil containing about 66%of caprolactam, 30.4% of water, 2.1% of ammonium sulfate, 0.4% ofammonia and 0.3% of cyclohexanone which caprolactam oil is obtained bythe Beckmann rearrangement of cyclohexanone oxime and subsequentneutralization, said process comprising the. steps of introducing saidcaprolactam oil into a heated reaction tube, and passing air heated toabout Q. and at a rate of about one hundred times the volume of saidcaprolactam oil through said reaction tube until said cyclohexanone,said ammonia and a portion of said water have been removed and saidcaprolactam comprises 75-76% of said caprolactam oil.

11. In a process as claimed in claim 10, wherein about 0.02% of anaqueous solution of manganese acetate of about 50% strength is added tosaid caprolactam oil prior to passing said hot air through said reactiontube.

12. A process for the preconcentration of a liquid containing about66-68% of a lactam, 28-31% of water, 1.4-2% of ammonium sulfate, 02-04%of ammonia and 01-03% of a ketone, comprising the step of reducing thecontent of said water and substantially removing said ammonia and saidketone by passing air through said liquid at elevated temperature untilthe content of said lactam in said liquid has risen to above 72% butbelow 80%.

13. A process for the preconcentration of a liquid containing about66-68% of a lactam, 28-31% of water,.

1.4-2% of ammonium sulfate, 0.2-0.4% of ammonia and 0.1-0.3% of aketone, comprising the steps of introducing said liquid into a reactiontube heated to about 100 C., and passing air through said reaction tubeat a rate of about 100 times the volume of said liquid per hour, untilsaidammonia and said ketone are removed and the content of said lactamin said liquid is above 72% but below 80%.

14. A process for recovering a lactam from a watercontaining lactam oilobtained by the Beckmann rearrangement of an oxime of a cyclic ketone,the subsequent neutralization and the extraction of said watercontaining lactam oil with a chlorinated hydrocarbon solvent, theimprovement which comprises passing a stream of a gas selected from theclass consisting ofa molecular oxygen containing gas and nitrogenthrough said water containing lactam oil at elevated temperatures untilthe water content thereof is reduced to a predetermined value, thetreatment with said gas stream being effected prior to the extractionwith said chlorinated hydrocarbon, whereby the formation of emulsionsduring said extraction step is avoided and the permanganate number ofsaid lactam is raised to a relatively high value.

15. A process according to claim 14 wherein said gas is nitrogen.

16. A process according to claim 14 wherein the temperature is kept atabout -110 C.

References Cited in the file of this patent UNITED STATES PATENTS

1. A PROCESS FOR THE PRECONCENTRATION OF WATER-CONTAINING LACTAM OILOBTAINED BY THE BECKMANN REARRANGEMENT OF OXIMES OF CYCLIC KETONES ANDSUBSEQUENT NEUTRALIZATION, COMPRISING THE STEP OF PASSING A STREAM OFAIR THROUGH SAID WATER-CONTAINING OIL AT ELEVATED TEMPERATURE UNTIL THEWATER CONTENT OF SAID OIL HAS BEEN REDUCED TO A PREDETERMINED VALUE. 14.A PROCESS FOR RECOVERING A LACTAM FROM A WATERCONTAINING LACTAM OILOBTAINED BY THE BECKMANN REAR RANGEMENT OF AN OXIME OF A CYCLIC KETONE,THE SUBSEQUENT NEUTRALIZATION AND THE EXTRACTION OF SAID WATERCONTAINING LACTAM OIL WITH A CHLORINATED HYDROCARBON SOLVENT, THEIMPROVEMENT WHICH COMPRISES ASSING A STREAM OF A GAS SELECTED FROM THECLASS CONSISTING OF A MOLECULAR OXYGEN CONTAINING GAS AND NITROGENTHROUGH SAID WATER CONTAINNG LACTAM OIL AT ELEVATED TEMPERATURES UNTILTHE WATER CONTENT THEREOF IS REDUCED TO A PREDETERMINED VALUE, THETREATMENT WITH SAID GAS STREAM BEING EFFECTED PRIOR TO THE EXTRACTIONWITH SAID CHLORINATED HYCROCARBON, WHEREBY THE FORMATION OF EMULSIONSDURING SAID EXTRACTION STEP IN AVOIDED AND THE PERMANGANATE NUMBER OFSAID LACTAM IS RAISED TO A RELATIVELY HIGH VALUE.